This invention relates to a wood golf club head and more particularly to a wood golf club head which improves the driving or flying distance of a hit ball and its directionality.
A golf club encounters air resistance when it is swung at the time of hitting of a ball and this results in the drop head speed and in a occurrence of irregular vibration of the club's shaft. The drop of the head speed in turn reduces the flying distance of the hit ball and irregular vibration of the club shaft effects directionality of the hit ball. Such phenomena occur particularly in a wood golf club head having a large club head and this tendency becomes all the more remarkable in those wood golf clubs whose head size becomes greater with a recent trend longer club shafts.
An analysis made by the inventors of the present invention reveals that the phenomena described above are mainly caused by layer separation of the air flow that flows on an upper surface side of the club head as shown in FIG. 13 of the accompanying drawings. FIG. 13 shows the air flows Q that occur around a wood golf club head 1 when it is swung from the left to the right in the drawing. The air flow Q flows in a direction relatively opposite to the moving direction of the wood golf club head 1, strikes a face 2 on the front surface of the club head 1, and is divided vertically into air flows Qa on the upper side surface 3 and air flows Qa on the sole side 4. Of these air flows, the air flow Qa flowing on the sole keeps the state side keeps the state is laminar because the sole surface is substantially horizontal but the air flow Qa flowing on the upper surface side undergoes layer separation of its laminar portion in the front half region of the upper surface 3 and generates large turbulent flows at the back of the position of the layer separation as shown in the drawing because the radius of curvature of the surface in the front half portion of the club head is greater than that of the sole. These large turbulent flows increase the air resistance to the wood golf club head 1 and greatly change the pressure distance between the upper surface side 3 and the sole side 4, thereby causing irregular vibration of the club's shaft.